Combine.AccumulatingCombineFn (Apache Beam 2.44.0)

java.lang.Object
- org.apache.beam.sdk.transforms.Combine.CombineFn<InputT,AccumT,OutputT>
- - org.apache.beam.sdk.transforms.Combine.AccumulatingCombineFn<InputT,AccumT,OutputT>

Type Parameters:: InputT - type of input values; AccumT - type of mutable accumulator values; OutputT - type of output values

All Implemented Interfaces:: java.io.Serializable, CombineFnBase.GlobalCombineFn<InputT,AccumT,OutputT>, HasDisplayData

Direct Known Subclasses:: ApproximateQuantiles.ApproximateQuantilesCombineFn, Top.TopCombineFn

Enclosing class:: Combine

public abstract static class Combine.AccumulatingCombineFn<InputT,AccumT extends Combine.AccumulatingCombineFn.Accumulator<InputT,AccumT,OutputT>,OutputT>
extends Combine.CombineFn<InputT,AccumT,OutputT>

A CombineFn that uses a subclass of Combine.AccumulatingCombineFn.Accumulator as its accumulator type. By defining the operations of the Accumulator helper class, the operations of the enclosing CombineFn are automatically provided. This can reduce the code required to implement a CombineFn.

For example, the example from Combine.CombineFn above can be expressed using AccumulatingCombineFn more concisely as follows:


 public class AverageFn
     extends AccumulatingCombineFn<Integer, AverageFn.Accum, Double> {
   public Accum createAccumulator() {
     return new Accum();
   }
   public class Accum
       extends AccumulatingCombineFn<Integer, AverageFn.Accum, Double>
               .Accumulator {
     private int sum = 0;
     private int count = 0;
     public void addInput(Integer input) {
       sum += input;
       count++;
     }
     public void mergeAccumulator(Accum other) {
       sum += other.sum;
       count += other.count;
     }
     public Double extractOutput() {
       return ((double) sum) / count;
     }
   }
 }
 PCollection<Integer> pc = ...;
 PCollection<Double> average = pc.apply(Combine.globally(new AverageFn()));

See Also:: Serialized Form

Nested Class Summary

Nested Classes
Modifier and Type	Class and Description
`static interface`	`Combine.AccumulatingCombineFn.Accumulator<InputT,AccumT,OutputT>` The type of mutable accumulator values used by this `AccumulatingCombineFn`.

Constructor Summary

Constructors
Constructor and Description

AccumulatingCombineFn()

Constructors
Constructor and Description
`AccumulatingCombineFn()`

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`AccumT`	`addInput(AccumT accumulator, InputT input)` Adds the given input value to the given accumulator, returning the new accumulator value.
`OutputT`	`extractOutput(AccumT accumulator)` Returns the output value that is the result of combining all the input values represented by the given accumulator.
`java.lang.reflect.TypeVariable<?>`	`getAccumTVariable()` Returns the `TypeVariable` of `AccumT`.
`Coder<AccumT>`	`getAccumulatorCoder(CoderRegistry registry, Coder<InputT> inputCoder)` Returns the `Coder` to use for accumulator `AccumT` values, or null if it is not able to be inferred.
`Coder<OutputT>`	`getDefaultOutputCoder(CoderRegistry registry, Coder<InputT> inputCoder)` Returns the `Coder` to use by default for output `OutputT` values, or null if it is not able to be inferred.
`java.lang.String`	`getIncompatibleGlobalWindowErrorMessage()` Returns the error message for not supported default values in Combine.globally().
`java.lang.reflect.TypeVariable<?>`	`getInputTVariable()` Returns the `TypeVariable` of `InputT`.
`java.lang.reflect.TypeVariable<?>`	`getOutputTVariable()` Returns the `TypeVariable` of `OutputT`.
`AccumT`	`mergeAccumulators(java.lang.Iterable<AccumT> accumulators)` Returns an accumulator representing the accumulation of all the input values accumulated in the merging accumulators.
`void`	`populateDisplayData(DisplayData.Builder builder)` Register display data for the given transform or component.

Methods inherited from class org.apache.beam.sdk.transforms.Combine.CombineFn
apply, compact, createAccumulator, defaultValue, getInputType, getOutputType

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - AccumulatingCombineFn
```
public AccumulatingCombineFn()
```
- Method Detail
  - addInput
```
public final AccumT addInput(AccumT accumulator,
                             InputT input)
```
    Description copied from class: Combine.CombineFn
    
    Adds the given input value to the given accumulator, returning the new accumulator value.
    
    Specified by:
    
    addInput in class Combine.CombineFn<InputT,AccumT extends Combine.AccumulatingCombineFn.Accumulator<InputT,AccumT,OutputT>,OutputT>
    
    Parameters:
    
    accumulator - may be modified and returned for efficiency
    
    input - should not be mutated
  - mergeAccumulators
```
public final AccumT mergeAccumulators(java.lang.Iterable<AccumT> accumulators)
```
    Description copied from class: Combine.CombineFn
    
    Returns an accumulator representing the accumulation of all the input values accumulated in the merging accumulators.
    
    Specified by:
    
    mergeAccumulators in class Combine.CombineFn<InputT,AccumT extends Combine.AccumulatingCombineFn.Accumulator<InputT,AccumT,OutputT>,OutputT>
    
    Parameters:
    
    accumulators - only the first accumulator may be modified and returned for efficiency; the other accumulators should not be mutated, because they may be shared with other code and mutating them could lead to incorrect results or data corruption.
  - extractOutput
```
public final OutputT extractOutput(AccumT accumulator)
```
    Description copied from class: Combine.CombineFn
    
    Returns the output value that is the result of combining all the input values represented by the given accumulator.
    
    Specified by:
    
    extractOutput in class Combine.CombineFn<InputT,AccumT extends Combine.AccumulatingCombineFn.Accumulator<InputT,AccumT,OutputT>,OutputT>
    
    Parameters:
    
    accumulator - can be modified for efficiency
  - getAccumulatorCoder
```
public Coder<AccumT> getAccumulatorCoder(CoderRegistry registry,
                                         Coder<InputT> inputCoder)
                                  throws CannotProvideCoderException
```
    Description copied from interface: CombineFnBase.GlobalCombineFn
    
    Returns the Coder to use for accumulator AccumT values, or null if it is not able to be inferred.
    By default, uses the knowledge of the Coder being used for InputT values and the enclosing Pipeline's CoderRegistry to try to infer the Coder for AccumT values.
    This is the Coder used to send data through a communication-intensive shuffle step, so a compact and efficient representation may have significant performance benefits.
    
    Specified by:
    
    getAccumulatorCoder in interface CombineFnBase.GlobalCombineFn<InputT,AccumT,OutputT>
    
    Throws:
    
    CannotProvideCoderException
  - getDefaultOutputCoder
```
public Coder<OutputT> getDefaultOutputCoder(CoderRegistry registry,
                                            Coder<InputT> inputCoder)
                                     throws CannotProvideCoderException
```
    Description copied from interface: CombineFnBase.GlobalCombineFn
    
    Returns the Coder to use by default for output OutputT values, or null if it is not able to be inferred.
    By default, uses the knowledge of the Coder being used for input InputT values and the enclosing Pipeline's CoderRegistry to try to infer the Coder for OutputT values.
    
    Specified by:
    
    getDefaultOutputCoder in interface CombineFnBase.GlobalCombineFn<InputT,AccumT,OutputT>
    
    Throws:
    
    CannotProvideCoderException
  - getIncompatibleGlobalWindowErrorMessage
```
public java.lang.String getIncompatibleGlobalWindowErrorMessage()
```
    Description copied from interface: CombineFnBase.GlobalCombineFn
    
    Returns the error message for not supported default values in Combine.globally().
    
    Specified by:
    
    getIncompatibleGlobalWindowErrorMessage in interface CombineFnBase.GlobalCombineFn<InputT,AccumT,OutputT>
  - getInputTVariable
```
public java.lang.reflect.TypeVariable<?> getInputTVariable()
```
    Returns the TypeVariable of InputT.
  - getAccumTVariable
```
public java.lang.reflect.TypeVariable<?> getAccumTVariable()
```
    Returns the TypeVariable of AccumT.
  - getOutputTVariable
```
public java.lang.reflect.TypeVariable<?> getOutputTVariable()
```
    Returns the TypeVariable of OutputT.
  - populateDisplayData
```
public void populateDisplayData(DisplayData.Builder builder)
```
    Register display data for the given transform or component.
    populateDisplayData(DisplayData.Builder) is invoked by Pipeline runners to collect display data via DisplayData.from(HasDisplayData). Implementations may call super.populateDisplayData(builder) in order to register display data in the current namespace, but should otherwise use subcomponent.populateDisplayData(builder) to use the namespace of the subcomponent.
    By default, does not register any display data. Implementors may override this method to provide their own display data.
    
    Specified by:
    
    populateDisplayData in interface HasDisplayData
    
    Parameters:
    
    builder - The builder to populate with display data.
    
    See Also:
    
    HasDisplayData

Class Combine.AccumulatingCombineFn<InputT,AccumT extends Combine.AccumulatingCombineFn.Accumulator<InputT,AccumT,OutputT>,OutputT>

Nested Class Summary

Constructor Summary

Method Summary

Methods inherited from class org.apache.beam.sdk.transforms.Combine.CombineFn

Methods inherited from class java.lang.Object

Constructor Detail

AccumulatingCombineFn

Method Detail

addInput

mergeAccumulators

extractOutput

getAccumulatorCoder

getDefaultOutputCoder

getIncompatibleGlobalWindowErrorMessage

getInputTVariable

getAccumTVariable

getOutputTVariable

populateDisplayData